\470 Chapter 26 · Energy Dispersive X-Ray Microanalysis Checklist

			from mass concentration (weight fraction) to atomic frac-
			tion or oxide fraction includes normalization.
		\3.\	DTSA-II provides an estimate of the measurement uncer-
	26
			tainty for each element. The estimate should make clear
			which factors were considered and whether the estimate
			should be considered an estimate of accuracy or just an esti-
			mate of precision. A measurement without an uncertainty
			estimate is open to misuse. The client may assume that the
			result is more accurate than it really is and draw conclusions
			that cannot be justified by the data. Alternatively, the client
			may not trust the data or may assume that it is less accurate
			than it is and fail to draw conclusions that are justified. Either
			way, data presented without uncertainties is of limited utility.
	\4.\		If the spectra represent a nominally homogeneous
			region (or one you suspect to be), add descriptive statis-
			tics (mean, standard deviation) summarizing the

variation­ between locations for each element. Compare this value with the uncertainty estimate for a single measurement to detect heterogeneity.

•  Conclusions

Conclusions should be pithy. You should be very careful only to report that which is directly supported by the measurement results. In other words, stick to the facts and avoid conjecture. Don’t answer questions that go beyond the data and your personal expertise.

Reference

International Organization for Standardization (2012) Standard file format for spectral data exchange ISO 22029:2012. 7https://www.iso. org/standard/56211.html

471		27

X-Ray Microanalysis

Case Studies

27.1\ Case Study: Characterization of a Hard-­Facing

Alloy Bearing Surface – 472

27.2\ Case Study: Aluminum Wire Failures in Residential Wiring – 474

27.3\ Case Study: Characterizing the Microstructure of a Manganese Nodule – 476

References – 479

© Springer Science+Business Media LLC 2018

J. Goldstein et al., Scanning Electron Microscopy and X-Ray Microanalysis, https://doi.org/10.1007/978-1-4939-6676-9_27

\472 Chapter 27 · X-Ray Microanalysis Case Studies

27.1\ Case Study: Characterization of a Hard-­ Facing Alloy Bearing Surface

Background: As part of a study into the in-service failure of the bearing surface of a large water pump, characterization was 27 requested of the hard-facing alloy, which was observed to have separated from the stainless steel substrate, causing the failure.

This problem illustrates the critical importance of careful specimen preparation of a macroscopic object with centimeter dimensions to locate regions of microscopic interest with micrometer dimensions. Metallographic preparation produced a polished cross section of an intact portion of the hard-facing alloy layer as deposited onto the stainless steel base, as shown in .  Fig. 27.1. SEM-EDS analysis with DTSA-II gave the results shown in .  Fig. 27.2 for the stainless steel base and at one location in the hard-facing alloy. EDS elemental mapping produced the images shown in

.  Fig. 27.3. The SEM-­BSE image (.  Fig. 27.1) revealed the presence of numerous voids that were predominantly located (white arrows) at the interface between the hard-facing alloy and the stainless steel substrate, with a smaller population of voids located within the hard-facing alloy (yellow arrows). The elemental maps (.  Fig. 27.3) revealed that the hard-fac- ing alloy layer had a very complex microstructure with distinct heterogeneity. The voids were found to be closely associated with regions with that had elevated Cr, both near the hard-facing alloy-stainless steel interface and within the hard-facing alloy. These voids severely compromised the performance of the bearing surface.

Complex fine-grained regions were also observed within the hard-facing alloy, as shown in the elemental maps in

.  Fig. 27.4 and the SEM-BSE image in .  Fig. 27.5, which shows strong atomic number contrast. SEM-EDS analysis with DTSA-II gave the results presented in .  Fig. 27.5, which confirm the gray scale sequence as a function of composition, with the sharp rise in W (see table in .  Fig. 27.5) dominating backscattering.

The information provided by SEM-EDS enabled metallurgists to modify the hard-facing alloy composition and deposition conditions to eliminate the void formation during deposition, producing satisfactory service behavior.

Stainless steel substrate

Voids

. Fig. 27.1  SEM-BSE image of the cross-section of a hard-facing alloy deposited on a stainless steel substrate. Note the voids at the interface between the hard-facing alloy and the stainless substrate (white arrows), as well as a smaller population of voids entirely within the hard-facing alloy (green arrows)

. Fig. 27.2  SEM-BSE image showing locations of SEM-EDS analyses with NIST DTSA-II

Si	Cr	Mn	Fe	Ni	Mo
0.0055	0.1818	0.0180	0.6507	0.1188	0.0266
±0.0001	±0.0007	±0.0002	±0.0015	±0.0008	±0.0002

200 mm

BSE MAG: 100 ´ HV: 20.0 kV WD: 11.0 mm

Si	Cr	Mn	Fe	Co	Ni
0.0377	0.0915	0.0006	0.0228	0.3859	0.4616
±0.0002	±0.0002	±0.0001	±0.0001	±0.0005	±0.0007

473

27

27.1 · Case Study: Characterization of a Hard-­Facing Alloy Bearing Surface

Ni

Co

Cr	Ni_Cr_Co	200 µm
. Fig. 27.3  Elemental mapping, with color overlay: Ni = red; Cr = green; Co = blue

Ni	W

Cr Ni_W_Cr

5 µm

. Fig. 27.4  Elemental mapping of an area of fine-scale grains